#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define int ll
const int inf = 1e18;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int, int> p2;
#define rep(i, high) for (int i = 0; i < (high); i++)
#define repp(i, lo, high) for (int i = (lo); i < (high); i++)
#define repe(i, container) for (auto& i : container)
#define sz(x) ((int)(x).size())
#define all(x) begin(x), end(x)
void gather(int u, vvi& adj, vi& value, deque<int>& arr)
{
arr.push_back(value[u]);
repe(e, adj[u]) gather(e, adj, value, arr);
}
signed main()
{
cin.tie(0)->sync_with_stdio(0);
int n, s;
cin >> n >> s;
vi nodevalue(n+1);
vvi adj(n+1);
rep(i, n)
{
int p, v;
cin >> v >> p;
nodevalue[i] = v;
if (p == 0) adj.back().push_back(i);
else adj[p-1].push_back(i);
}
nodevalue.back() = s;
vector<deque<int>> children;
repe(e, adj[n])
{
children.push_back({});
gather(e, adj, nodevalue, children.back());
}
int ans = nodevalue.back();
while (true)
{
bool any = false;
repe(c, children)
{
int p = ans;
int k = -1;
rep(i, sz(c))
{
p += c[i];
if (p < 0) break;
if (p > ans)
{
k = i+1;
break;
}
}
if (k!=-1)
{
any = 1;
ans = p;
rep(i, k) c.pop_front();
}
}
if (!any) break;
}
cout << ans-nodevalue.back();
return 0;
}
